Acoustic instrument



May 6, 1930. H. c. HAYES ACOUSTIC INSTRUMENT Filed April 13, 1925 3 Sheets-Sheet l Quinn H06 y 1930- H. c. HAYES 1,757,938

ACOUSTIC INSTRUMENT Filed April 1a, 1925 5 Sheets-Sheet 2 5 nventoz attoznug H. c. HAYES 1,757,938

5 Sheets-Sheet 3 mventoz ACOUSTIC INSTRUMENT Filed April 13, 1925 Patented-MM 1930' UNITED STATES PATENT OFFICE I mam c. Earns, or vvAsnmero n; nrs'rnrcr or connimm v v I ncous'rrc msrnumnnr Application and Apri1 13, 192 5. Serial Ira-22,637. v v umran unnnn'rnn sor er manor: 3, 1883, Asnnnnnnn Arms 30, 1928; 370 o. e. 157) My invention relates broadly to acoustic I My invention will be more fully under--v instruments and more particularly to sound stood from'the specification hereinafter fol reproducing devices employing diaphragms lowing by reference to the accompanying which are driven by electro-magnetic means, drawings, in which: 1

and still more particularly to methods and Figures 1 and 2 show side and front view 55 means for reducing the intensity of the .varirespectively of a conical diaphragm attached ous resonant frequencies to approximates about its periphery to a ring shaped mounti equality with the other or non-resonant freing leaving the diaphragm exposed on both quencies so as to render the intensity of the sides; Fig. 3 shows schematically that the sound output from the diaphragm substansound generated on opposite sides of the diae0 tially uniform and independent of the frephragm is a half-wave length out of phase;.

- quency over the working audible range or Fig. 4 is a cross sectional view of one of the any predetermined portion thereof. practical embodiments'of my invention, show- One of the objects of my invention is to ing the provision of a frequency absorbent increase the radiation of all frequencies from material adjacent the rear of the diaphragm on one side of a sound generating diaphragm for securing the advantages which accrueby through the reaction thereon of the radiathe use of my invention; Figs. 5 andfi show tion from the other side of the diaphragm, characteristic curvespf conical diaphra thereby causing the diaphragm to generate constructed in accordance with my invenpractically the same intensity from one side tion; and Figs. 7 and 8 show one ofthe'p'racw 7 s that it normally would from both sides, if tical embodimentsof my invention in a coni they were both allowed to radiate into space. cal diaphragm sound reproducer; and Figs.

Another object of my invention is to ro- 9 and 10 show'still another embodiment of vide a conical diaphragm sound reprodigcer my Invention.

in which a selected frequency range of sound The intensity and quality of the sound .75 vibrations may be reproduced to give subheard at'any poi t away from a diaphragm 'stantially uniform intensity. which radiates sound on both sides is depend- Still another object of my invention is to ent upon the sum total or the sound ori provide an arrangement of conical diaphragm hating on each of the two sides of the diasound reproducerin which radiation from the phragm and both the intensity and quality so front of the conical diaphragm may be in- Y are adverselyaifected through the process of creased while preventing the radiation of twa'veinterference. Moreover, th'eefiect upon sound vibrations from the rear of the diathe earof such'a sound reproducer is unsatphragm to prevent the radiation of undeisfactory and unpleasant for the reason that sired frequencies. the sense of direction operateswith diculty a5 A still further object of my invention is because the sound does not come from a sinthe provision of an absorbent for undesired gle source-but from two distinct sources, one frequencies in relation to aconical diaphragm on each side of the diaphragm, and while sound reproducer which absorbent may take" these two sounds are practically identical as 7 0 the form of a filter or reflecting surface 'ar regards location, nevertheless; so far as the to ranged parallel'to the rear of the conical diasense ofidirection is concerned they are well phragh at a distance which maybe varied to' separated because they generate sound en- 'select the desired frequencies for efficient re tirely out ofvphase. By my invention ll proproduction. *vide a. diaphragm construction which radi- My invention finds application: to large ates sound free from undesired frequencies as conical diaphragms utilized in the reproduc from one side only of the diaphragm. 1

tion of sounds and will'be described infeon- Referring more particularly to the draw- Y nection with such diaphragms although it ings, reference character 1 designates a cylin a will be understood that the'invention is also drical frame having a concentric ring 2 suapplicable 'to' other types of diaphragms. vperimposed thereon for securing a relatively M the construction of sound reproducers heretofore employed where emanations of sound occur from opposite sides of the diaphragm. The diaphragm emanates sound represented diagrammatically by reference characters 4 and 5 fromthe front thereof and siin'ulta-v neously sound Waves displaced 180 are emanated from the rear of the diaphragm 3, as indicated at 6 and 7. By reason of the phase displacement of the sound emanations there.

will he places indicated at the apex 8 of dotted lines 9 and 10 and the apex 11 of dotted lines %2 and 14 where the emanations will interere.

Figure 4 shows an embodiment of my invention wherein the conical diaphragm 3 is shown clamped between ring shaped members 1 and 2 and one side thereof closed by a wall 15 for preventing radiation of sound from the rear of thediaphragm. Numerals 4 and 5 represent the sound waves radiated from the left or from the exposed side of the diaphragm, and 6 and 7 represent the sound waves generated on. the opposite side of the diaphra m. This side of the diaphragm is enclosedv rom open space by member 15 which is a heavy inert material. Numeral 16 represents an electromagnetic device which drives the diaphragm through link 17 connecting tothe center of the cone by small conical members 13. Member 20 is made of a particular sound insulating material, the nature and function of which is dependent upon the physical characteristics of the diaphragm and its driving mechanism and which can be best understoodby first assuming .it to be made of a material that absorbs no sound energy. Under such conditionsthe sound waves represented by 6 and 7 will repeat back to the diaphragm and either help or hinder its motion, depending upon the phase'relation. .If the path'of travel from the diaphragm to member 20 and back again is less than one-half of the wave length of. the highest pitch sound the diaphragm is called upon togenerate, then the reflected wave will always aid the diaphragm on its outward movement and since the energy ra-- diated from the enclosed side of the dia-. phragm is, barring small viscosity losses, all

given back'a ain to the diaphragm its amplitude will increase until the sound generated from the exposed side aloneis practi-' callyequal to the sound generated from both described is superior to that represented by Figs. 1, 2 and 3. Its sensitivity is fully 'as high and the quality of the sound is better for reasons already stated herein. It still retains one serious defect also contained in the unenclosed diaphragm,viz.: The. sound output will be abnormally intense for those frequencies at which the diaphragm or the driver or the combination are mechanically resonant. The purpose of member 20 is to weaken the sound output of these resonant frequencies, and Figs. 5 and 6 illustrate how this is accomplished. In Fig. 5, curve 21 shows the general form of the intensity and frequency curve for a certain type of loud speaker, the ordinates ofthe curve representing the intensity and the'abscissae representing the frequency, where the diaphragm radiates from both sides.

This is also approximately in the form of the same curve for the enclosed diaphragm as in Fig. 4 and member 20 made of a material having an absorption coeflicient so 7 small as to be negligible. Now suppose member 20 to be a perfect absorber for ,all frequencies between 50 and 4000 cycles. The intensity curve will be represnted by the broken line 22 havin ordinates equal to approximately one-hal the full line curve, for

where between curves 21 and 22 of Fig: 5, and

the ratio of the ordinates will not be constant as shown. If the material were such that its absorption coeflicient were greatest for the range of frequencies included between frequencies 400 to 1600 cycles of Fig. 5, and

small for the frequencies represented by both ends of these curves, then the shape of the resulting intensit curve would be much more favorable since t e higher arts of the curve would be reduced while the ower parts would be affected very much less in proportion.

. By preventing any small band of frequencies from reflecting back to the diaphragm'.

within the sound chamber it is ossible to reduce the diaphragm output or such fre- .quency b about 50 per cent. Any frequency that is a sorbed or removed from t-he'chamber by any other method, as for instance, an

acoustical filter illustrated more clearly in and id'its motion. Thus the decrease in 1ntensity of output for any frequency is. equal to one-half the energy absorbed at that frequency and therefore, the present decrease is equal toone-half the coefiicient of absorption of the member 7 and 8, will not reflect to the diaphragm I 20.for sound of that fre- 1 Fig. tigives a concrete example showing how the final output from a reproducer such as shown in principle in Fig. 4-is modified by the presence of the absorbent 20. Curve 23 gigs the output with member '20 removed.

ve 24 shows the coeflicient of absorption as a function of the -frequency. Curve 25 shows the output intensity plotted against frequency with the absorbent 20 in position. While the combination does not make the intensity uniform irrespective of frequency it does make it more nearly uniform and makes the reproduction noticeably better.

In Figs. 7 and 8 the ring shaped member or casing 1 has been extended to receive a series of resonant chambers 37 formed in a circular late 36. The circular plate 36 is positioned intermediate plates 34- and 38. Plate 34 has a plurality of apertures 35 concentric with the chambers 37 while plate 38 has apertures 39 disposed along a central axis with respect to chambers 37. The assembly of resonant chambers as illustrated provides a filter system for undesired freqpencies wherein undesired frequencies are a sorbed and dissipated and not radiated as sound. I

In Figs; 9 an 10 I have shown the ring member or casing 1 extended and screw threaded at 30 to receive a rear closure member 31 which may be varied in position with respect to the rear of the diaphragm 3, to such positions as are shown by dotted lines 32 by means of a suitable tool inserted in sockets 33 i the length of the .By regulating in the rear of the plate 31. By adjusting the sition of the plate..31 I am able to change path travelled by the sound emanating from t e rear of the diaphragm 3.

this distance I am able to annul the undesired frequencies while the desired frequencies may be reproduced. The chamber which encloses the rear side of the diaphragm 3 is so designed and dimensioned that for sound waves therein havin the same frequency as those which are und y weak in the neral sound out ut from the instrument, the path of trave to the chamber wall 31 and return shall be such that those waves will reflect back and meet the diaphragm in phase. Undesired uencies are annulled by proportioning the path of travel to be equal to one wave len h whereby the reflected frequency es the initially generated frequency one half wave length out of phase opposite such frfincies.

'le I have illustrated my invention in certain'embodiments I desire that it be understood that I intend no limitations upon the invention but that the principle of my invention may be applied m various ways and the advantageous results hereinset forth obtained by various constructions of filters, absorbents and other mechanical arrangements associated with the sound reproducing diaphragm and that no limitations upon the from the diaphragm invention are intended other than are impurposes without the payment to me of any royalty thereon or therefor.

, Having thus described my invention, what I claim and desire to secure y Letters Patent of the United States is as follows:

1. In an acoustic instrument comprisin a sound reproducing diaphragm, a driver %or v imparting sound vibrations to the diaphragm,

a casing secured to the peri hery of the diaphragm and forming a cham ber enclosing one side of said diaphragm, and means associated with the chamber forregulating, and apportioning through selective reactan'cethe extent of the radiation of the various frequencies of the sound ener radiated from the exposed side of the diap ragm; I

2. An acoustic instrument comprising a sound reproducing diaphragm, a driver for imparting sound vibratlons to the diaphra m, a casing secured to the periphery of the 'aphragm and forming a chamber enclosing one side of thediaphragm, the chamber having such proportions that for sound waves im arting sound vibrations'to the diaphragm,

an a selective frequenc absorbing'and re;

fleeting medium mounte adjacent to one side of the diaphragm for selectively absorbing and reflecting sound waves produced by the diaphragm.

. 4. An acoustic instrument comprising a i a driver for sound reproducing diaphragm,

a cham-' imparting sound vibrations thereto, ber enclosing one from the resonant frequency of ,the' diaphragm the path of travel from the dia 'hragm to the chamber wall and return shall such that those waves are reflected back and meet the diaphragm in phase.

5. An acoustic instrument comprising in combination asound reproducing diaphragm a driver imparting sound vibrations thereto, a chamber enclosin phragm and means or varying the effective depth of said chamber for the selection of a depth with which undesired frequencies emanating from said diaphragm may be annulled while desired frequencies may be reinforced and radiated from the other side of said dia- HABVEY C.

side of the diaphragm and dimensioned so that for sound waves therein having a frequency lying at avalue removed one side of said dia- 

